Internally heated autoclave for metal impregnation

ABSTRACT

An internally heated autoclave includes an outer shell having therein two separate and isolated chambers. The first chamber is a heating chamber and has therein a heating means. The second chamber is an impregnating chamber and has therein an impregnating vessel adapted to contain molten metal. A dip cage containing a porous article to be impregnated by the molten metal is attached to the shaft of a lift means and is adapted to be raised and lowered in the impregnating chamber. Both of the chambers may be selectively connected to either a source of pressure or a source of vacuum. Means are provided to equalize the pressure within both chambers.

United States Patent [72] Inventors Toshikatsu Ishikawa Tokyo;

Munenori Tomoeda, Tokyo; Toyonosuke Kanemaru, Zushi, all of, Japan Primary I-Ixuminrr -Murris Kzlplzm AIInrm-y 'WcmlcmilL Lind and Pollack ABSTRACT: An internally heated autoclave includes an outer shell having therein two separate and isolated chambers. The first chamber is a heating chamber and has therein a heating means. The second chamber is an impregnating chamber and has therein an impregnating vessel adapted to contain molten metal. A dip cage containing a porous article to be impregnated by the molten metal is attached to the shaft ofa lift means and is adapted to be raised and lowered in the impregnating chamber. Both of the chambers may be selectively connected to either a source of pressure or a source of vacuum. Means are provided to equalize the pressure within both chambers.

0 pkgu 4 l /2 i p 21, a: 4/ K 6 III I,-

PATENTEU AUG 1 7 |97| SHEET 1 UF 2 Fig.4

Fig. 6

INVENTORS, TOSH/MTSU ISH/KAWA BY MUNENOR/ TOMOEDA TOYONOSUKE MNEMARU MMzzam WM Fig. 5

PATENTED ms 1 1 l9?! SHEET 2 OF 2 Fig. 7

IN VENTOR. TOSH/KATSU ISHIKA WA MUNENORI TOMOEDA Y TOYON05UKE KANEMARU viated.

In general, a molten metal impregnation autoclave apparatus ,of the above type must have the properties of resistance to corrosive and heat and be able to withstand high pressures. However, it has been very difficult to design and provide prior art autoclaves with all of the above properties.

In order to provide the autoclave with heat resistance, par ticular care should be taken to select the most suitable material of construction. For example, in reference to a metal material, carbon or alloy steel tends to be corroded by a corrosive metal such as antimony, therefore it cannot be used.

In view .of the above fact, the present inventors, have adopted the use of a crucible made of a graphite material which is resistant to corrosion of substantially all metals and alloys. The inventors have thus overcome the problem in connection with corrosion as well as heat resistance by the use of the graphite crucible for holding molten metal therein. Furthermore, a problem in connection with the use of the graphite material, that is, the pressure resistance of the graphite crucible, is overcome it by the provision of a novel construction wherein'a chamber including the graphite crucible and another chamber including a heating means are separated and insulated from each other within a cylindrical autoclave body, and further wherein the pressure in these two chambers is equalized.

It is an object of the invention to provide an improved autoclave for impregnating carbonaceous product with a molten metal under pressure in which a crucible for holding the molten metal is made of graphite so as to prevent it from being corroded.

It is another object of the invention to provide an autoclave in which an impregnating chamber including the crucible is completely separated from a heating chamber.

Itis still another object of the invention to provide an autoclave wherein each of the two chambers can be pressurized separately and independently during the impregnating process, and.further wherein the pressures prevailing in the impregnating chamber and the heating chamber can be equalized so that the crucible made of graphite can be subjected to a high pressure without damage.

Other objects and advantages of the invention will be apparent from the following description, which, taken in connection with the accompanying drawings, discloses a preferred embodiment thereof.

FIG. I is ahsectional view of the autoclave apparatus constructed in accordance with the principle of this invention.

FIG. 2 is a simplified view showing two separate chambers to be pressurized.

FIG. 3 is a view showing a first step of the impregnating process of this invention.

FIG. 4 is a view showing a second step wherein a blank is dipped in molten metal.

FIG. 5 is a view showing a third step.

FIG. 6 is a view showing a fourth step.

FIG. 7 is a perspective view of the autoclave of FIG. 1.

An outer shell 1 of the impregnating apparatus of this invention is lined with a heat insulator 2 at the inner side thereof in order to protect the apparatus when exposed to both high temperature and high pressure during the impregnating process. The heat insulator can be selected from the group consisting of ordinary refractory heat insulating bricks, carbonaceous material, carbonaceous fiber, graphite fiber, and ceramic fiber. However, carbon black is not suited for the purpose in view.

A heater 3 is installed within and spaced from the heat insulator 2. A metallic vessel 4 is concentrically disposed within the heater such that it separates a heating chamber 6 without the vessel from an impregnating chamber 5 without the vessel.

A beakerlike impregnating vessel or crucible 7 made of a heat-resistant impermeable graphite material is also concentrically disposed within the metallic vessel 4. Molten metal 8 is placed in the crucible 7.

The outer shell 1 is provided at its outer periphery with a cooling chamber 9 in order to cool the shell 1 to protect it against intense heat when both chambers 5 and 6 are heated to an elevated temperature during the impregnating process.

The source (not shown) of inert gas and a vacuum pump are connected through a valve 12 and a conduit 10 to the impregnating chamber 5 and through valves 12 and 11 to the heating chamber 6 such that both chambers 5 and 6 may be either pressurized or evacuated.

A lift means 13 is provided above the apparatus in such manner that its shaft 14 extends into the impregnating chamber 5. To the lower end of the shaft 14 is fixed a dip cage 15 of pyrolytic graphite. To control the temperature in the reactor a plurality of thermocouples 16 are secured thereto as shown in FIG. 1.

The crucible or impregnation vessel 7 is made of graphite material. The graphite material should have the following properties to meet the requirements of the impregnation process:

1. a mechanical strength sufficient to hold a relatively mol ten metal;

2. a good thermal conductivity and a dense structure to transfer heat sufficient to melt the metal; and

3. an appropriate impermeability to prevent vapor of the molten metal in the crucible from corroding components outside the crucible by permeating through the graphite structure.

In impregnating a porous material, such as, a carbonaceous or sintered product with molten metal in accordance with the present invention, the requirements thereof are described as follows: the temperature of a molten metal should be about 50- C. higher than its melting point; when the pressure is reduced, it should be at 10 -10 mm.Hg. and held for a period of 10-30 minutes; when the pressure is increased, it should be at 50-150 kg./cm. and held for a period of 10-30 minutes.

It is understood that the above requirements are exemplary only, not limiting.

A metal adapted for impregnating can comprise one metal or alloy having a melting point of about 600 to 1, 1 00 C., and another metal or alloy having a melting point of less than 600 C. Thus, an impregnating metal or alloy includes:

Melting Point, C.

Antimony 630 Aluminum 660 Cerium 804 Germanium 937 Silver 960 Copper 1,083 Antimony-T in alloy 425 Y alloy 630 In reference to the impermeability of graphite, it is affected by the wettability, viscosity, and surface tension of the molten metal for use in impregnation. Particularly, when a metal such as aluminum or antimony is used, a heat resistant impermeable graphite material having a very low permeability. of less than 10 cm. per second should be used. However, when a metal such as magnesium or silver is used, a graphite material having a low permeability in the order of 10-10 cm. per second can be employed.

Thus, the graphite material for use in the impregnating vessel has the following properties:

L76 or more 90xl0 ohm-cm. or less 320 kgJcm. or more l l0" cm./sec.

Bulk Density Electric Resistivity Flexural Strength Permeability cylindrical. However, the use of the impregnating vessel made of a graphite material having the above properties in a prior autoclave wherein a high pressure is applied is not feasible.

Therefore, the autoclave of this invention includes two concentrically disposed chambers, a heating chamber and an impregnating chamber insulated from each other. The impregnating vessel 7 of graphite material is placed within the impregnating chamber 5 and is surrounded by the inner wall of the concentrically disposed metallic vessel 4. Vessel 4 separates the heating chamber from the impregnating chamber, and at the same time supports the impregnating vessel 7. The metallic vessel 4 is placed between the impregnating vessel 7 and the heating means 3 disposed in the heating chamber 6 so that the metallic vessel 4 is heated by the heating means to an elevated temperature, but does not serve as a pressure vessel. Thus, the metallic vessel holds the impregnating vessel and separates the impregnating chamber from the heating chamber.

Accordingly, the molten metal is placed in the impregnating vessel within the impregnating chamber and is not in direct contact with the other parts of the autoclave apparatus, hence it never happens that a vapor from the molten metal corrodes the heatingwire of the heating means disposed in the heating chamber.

However, the metallic vessel is not sufficiently strong to resist both high temperature and high pressure during the impregnating process. Therefore, the apparatus of this invention applies a superatmospheric pressure in the impregnating chamber but also equalizes the pressure between the impregnating chamber and the heating chamber.

To this end, a conduit system in a simplified diagram is shown in F lG. 2 showing a bifurcated conduit system at the left and a double-conduit system at the right. FIG. 2 shows that the bifurcated system includes a single-conduit 10 to the source of gas. As the impregnating chamber A is completely separated from the heating chamber B, the above conduit system can be effected.

Thus, a source of gas, such as inert gas, is connected to a bifurcated conduit, one end of which is connected to the impregnating chamber, and the other end of which is connected to the heating chamber. A conduit system is provided in such manner that a selector valve 12 is installed at the outlet of thegas source while a valve 11 is installed at the inlet of the heating chamber. As a result, when the selector valve 12 is opened during the impregnating process, the inert gas is simultaneously supplied into theimpregnating chamber and the heating chamber, to equalize the pressure prevailing in both chambers, and further, when the valve 11 at the inlet of the heating chamber is closed,-the pressure in the impregnating chamber can be maintained at a desired high level.

The above conduit system has been shown as an example only, and is not meant to be limiting. It is understood that any conduit system can be used as long as the pressure between the impregnating chamber and the heating chamber is equalized at the time of pressure application.

When a blank is to be impregnated with the molten metal, it is dipped into the molten metal in the impregnating chamber by the aid of lift means 13 provided above the autoclave apparatus. In this case,.it is preferable to extend the shaft 14 of the lift through the cover 17 of the autoclave into the impregnating chamber and to fix a dip cage in which the blank is placed to the downward end of the shaft.

A material adapted for the dip cage can be any resistant to corrosion by the molten metal. Particularly, a pyrolytic graphite having the following properties is most suitable, because it is easily worked and a thin sheet thereof has sufiicient strength. Also, it has no wettability with a corrosion as well as heat-resistant metal.

Bulk Density: 2.2 Electric Resistivity: 40x10" ohm cm. Flexural Strength: 1,400 kgJcm.

In general, the dip cage is a cage provided with a number of slits at the sides and bottom thereof so as to let the molten metal thereinto freely when dipped therein. It is understood that if the blank is large, it may be directly clamped to the end of the lift shaft 14 without recourse to the dip cage.

In operation, molten metal8 is fed into the crucible or impregnating vessel 7 made of a heat-resistant impermeable graphite. A blank or a plurality of blanks to be treated are placed in the dip cage 15. At first the dip cage 15 is raised upwardly by the aid of the lift 13. In this state, inert gas, such as nitrogen or argon, is introduced through the selector valve 12 into the impregnating chamber 5 from the gas source, whereby the inert gas replaces the oxidizing gas therein soas to prevent the metal and the blank from oxidizing. This is shown in FIG. 3. Then, the heater 3 is heated by supplying electric energy thereto to heat the vessel or crucible 7 through the metallic vessel 4. i

The metal 8 for impregnating is thus melted by the heat of the heater 3. On reaching a temperature adapted for impregnating the metal, the chamber 5 is reduced in pressure by operating the selector valve 12. It is to be understood that the heating may take place while reducing the pressure if desired.

On reducing the pressure sufficiently, the shaft 14 is lowered by the lift 13 to dip the dip cage 15 into the molten metal 8 (FIG. 4).

Then, the valve 11 is opened to communicate the chamber 6 with the chamber 5 by the conduit 10 so that the inert gas under pressure may be fed into the chambers 5 and 6 by actuating the selector valve 12. Thus, the chambers 5 and 6 are pressurized to a sufficient level for impregnation. On reaching the desired pressure, the porous blank is held for a period of time by closing the valves 11 and 12 till it is impregnated with metal as shown in FIG. 4.

Next, the valve 12 is opened to exhaust the inert gas from the chamber 5 to return it to atmospheric pressure, and at the same time the valve 11 is opened to exhaust the inert gas from the chamber 6 to return it to normal pressure. Prior to solidification of the molten metal 8, the blank in the cage dipped in the molten metal is raised upwardly by the lift 13 to remove any excess metal attached thereto as shown in FIGS. 5-6.

FIG. 5 shows that the impregnating vessel is under pressure and the blank impregnated with the molten metal is cooled while under pressure in order to prevent the molten metal penetrated into the blank from exuding therefrom. If the high pressure in the impregnating chamber returns to normal pressure too quickly, there is some danger that the molten metal penetrated into the blank may exude. On the other hand, where there is no danger that the molten metal may exude from the treated blank, the blank impregnated with the molten metal may be cooled under normal pressure as shown in FIG. 6.

Finally, the cover 17 is opened to remove the blank impregnated with metal from the dip cage 15.

It is understood that the selecting time and selecting order of valves 11 and. 12 and the on and'off operation of heater 3 depend upon the material to be impregnated and the metal for impregnation.

The details of the autoclave in accordance with a preferred embodiment of the invention are described hereinbelow for exemplary purposes only, and are not intended to be limiting:

370 mm. in diameter X 1000 mm. height,ubout IOOIiters (r-Mo-Stainless Steel,

Capacity Material of Pressure Vessel We claim:

I An internally heated autoclave for impregnating a porous v V 35-70 mm. thick material with molten metal comprising an outer shell having if f 'j' 5 an open end and a closed end, a cover closing said open end, i CIVIL'C ClIlpCl'll lllc r a Maximum Temperature ol'lnncr Wall 425 C. cqolmg means posnlon?d for coolnflg the other penphery of Mnximum a- 150 kgycmy said shell, the inner periphery of said shell being lined with a Reduced Pressure 0.05 Torr. thermally insulating material; a metal vessel positioned conscrvi centrically within the interior of said shell and dividing said inl 35 i lo terior into two separate and isolated chambers, the first of said Heating Element Ni-Cr wire embedded m a chamotte refractory, 200 z2 w, chambers being a heating chamber between the outer 2 $53 Nlsmmless Steel periphery of said metal vessel and said shell, and the other of said chambers being an impregnating chamber formed by said metal vessel; an impregnating vessel positioned within and supported by said metal vessel, said impregnating vessel b Though i f gs i g f zi 33: adapted to contain said molten metal; heating means posigr p m er a o n e 00 tioned within said heating chamber for heating said metal vesthls y i can apply to other porous materials Such sel and thus said molten metal; a lift means having a shaft exceramlc and F P tending through said cover and into said impregnating when a mammal {mprcgnated m for examp a 20 chamber; a dip cage attached to the lowermost end of said carbonaceous mammal treated with antimony was used for shaft and adapted to be raised and lowered by said lift means; f for a {nechamcal Seal F use m a rotary part of a a pressure source; a vacuum source; and means to selectively hlgh'pressure f macihmet Such as flpompressolr communicate either said pressure source or said vacuum under the Severe 'f of i Pressure or h1g1? f source to said chambers, said means to communicate includhas been ascertained that it exhibits excellent lubricity as well 2 ing pressure equalization means to equalize the pressure in as a high sealing ability. Said Chambers.

The results of a comparison test conducted on the carbonaceous and graphite materials treated with this invention 2. In an autoclave as claimed in claim 1 wherein said im-. and the same materials untreated are shown as follows: pregnating vessel is made of graphite.

Electric Flexural Impregnating Bulk resistivity, Shore strength metal density ohm-cm. hardness kgJcmJ carbonaceous material.. Antimonym 2.55 1%?)(10- 108 1, 200

Do Y nllo 2. 10 {38)(10- 105 1, 670 Graphite material. 4. 71 x10- 4B0 Cm'bonacoous mute 1.70 37.5)(10- 95 Bill) umphito nmtorinl l. 70 90x 10- to 250 While the preferred embodiment of the present invention 3. In an autoclave as claimed in claim I wherein said dip has been shown and described herein, it is obvious that many cage is made olpyrolytic graphite. structural details may be changed without departing from the 40 spirit and scope of the appended claims. 

1. An internally heated autoclave for impregnating a porous material with molten metal comprising an outer shell having an open end and a closed end, a cover closing said open end, cooling means positioned for cooling the other periphery of said shell, the inner periphery of said shell being lined with a thermally insulating material; a metal vessel positioned concentrically within the interior of said shell and dividing said interior into two separate and isolated chambers, the first of said chambers being a heating chamber between the outer periphery of said metal vessel and said shell, and the other of said chambers being an impregnating chamber formed by said metal vessel; an impregnating vessel positioned within and supported by said metal vessel, said impregnating vessel adapted to contain said molten metal; heating means positioned within said heating chamber for heating said metal vessel and thus said molten metal; a lift means having a shaft extending through said cover and into said impregnating chamber; a dip cage attached to the lowermost end of said shaft and adapted to be raised and lowered by said lift means; a pressure source; a vacuum source; and means to selectively communicate either said pressure source or said vacuum source to said chambers, said means to communicate including pressure equalization means to equalize the pressure in said chambers.
 2. In an autoclave as claimed in claim 1 wherein said impregnating vessel is made of graphite.
 3. In an autoclave as claimed in claim 1 wherein said dip cage is made of pyrolytic graphite. 